Originator: Complex Systems Research Center, University of New Hampshire

Abstract:
Digital Elevation Model (DEM) is the terminology adopted by
the USGS to describe terrain elevation data sets in a
digital raster form. The standard DEM consists of a regular
array of elevations cast on a designated coordinate
projection system. The DEM data are stored as a series of
profiles in which the spacing of the elevations along and
between each profile is in regular whole number intervals.
The normal orientation of data is by columns and rows. Each
column contains a series of elevations ordered from south
to north, with the order of the columns from west to east.
The DEM is formatted as one ASCII header record (A-
record), followed by a series of profile records (B-
records) each of which includes a short B-record header
followed by a series of ASCII integer elevations per each
profile. The last physical record of the DEM is an accuracy
record (C- record).
The 7.5-minute DEM's provided through GRANIT are standard USGS
7.5-minute files reprocessed to conform to GRANIT standards, as
described below. The elevation values are reported in feet,
and are spaced at 30-meter intervals along and between
each profile.